Fluorescent lamp phosphors which emit white light may be comprised of phosphors which emit in the red, blue and green spectral regions. Magnesium tungstate is a blue-emitting fluorescent lamp phosphor which may be blended with manganese-activated zinc silicate, a green-emitting fluorescent lamp phosphor, and tin-activated strontium orthophosphate, a red-emitting fluorescent lamp phosphor, to produce a white-emitting fluorescent lamp phosphor.
The interior surface of a fluorescent lamp envelope is coated with a phosphor which has been suspended in an organic or aqueous binder. Many fluorescent lamp phosphors, including manganese-activated zinc silicate and tin-activated strontium orthophosphate, are readily dispersed in such binders and are said to have "stir-in" capability. However, some fluorescent lamp phosphors, such as magnesium tungstate, have a very fine particle size and tend to agglomerate when mixed into the binder. Because of this tendency to agglomerate, the binder suspension containing such phosphors must be milled to provide a smooth coating on the inside walls of a fluorescent lamp envelope. Such milling adds time and expense to the phosphor manufacturing and blending process.
It would be an advancement in the art to eliminate the milling requirement by providing a method for improving the dispersability of fine fluorescent lamp phosphors in aqueous and organic binder suspensions.
Latex polymers and copolymers have been used with cathode ray tube phosphors as binding agents to bind pigments to the phosphor particles. The pigments act as a filter to improve the color purity and contrast of the emitted light. U.S. Pat. No. 4,859,497 to Wolfe et al. describes a method of coating a silver-activated zinc sulfide cathode ray tube phosphor with a latex polymer to bind pigments to the phosphor particles and impart stir-in capabilites thereto.